Bitumen recovery from oil sands presents technical and economic challenges due to high viscosity of the bitumen at reservoir conditions. Steam assisted gravity drainage (SAGD) provides one process for producing the bitumen from a reservoir. During SAGD operations, steam introduced into the reservoir through a horizontal injector well transfers heat upon condensation and develops a steam chamber in the reservoir. The bitumen with reduced viscosity due to this heating drains together with steam condensate along a boundary of the steam chamber and is recovered via a producer well placed parallel and beneath the injector well.
However, costs associated with energy requirements for the SAGD operations limit economic returns. Accumulation in the reservoir of gaseous carbon dioxide (CO2) and/or solvent that may be injected with the steam in some applications can further present problems. For example, the gaseous CO2/solvent acts as a thermal insulator impairing heat transfer from the steam to the bitumen, decreases temperature of the drainage interface due to partial pressure impact, and decreases effective permeability to oil as a result of increased gas saturation.
Therefore, a need exists for methods and systems for recovering hydrocarbons from oil sands with an efficient steam-to-oil ratio.